The common conception of cells is that they are blebby sorts of things, amoeba-like, floating in a nutrient soup with everything they need to survive safely contained within their membrane. Maybe an illustration from a biology textbook is coming to mind even now.
Neurons aren’t like that at all. Yes, they have a round, blebby center, but shooting out from that center are long torturous processes, one to receive information (dendrites) and one to send out information (the axon). These processes can be as long as several feet–as long as the distance from the end of your big toe to the base of your spine.
A neuron’s sole reason for being is to receive information, integrate it, then pass it along. To do this, it must join with other neurons in a network. A lone neuron sends out those processes–searching, grasping fingers looking for a mate. Most of the time the neuron will only find rejection. You see, it cannot pair with just any other neuron. It must find the right one.
So those fingers continue on, listening for the call that says, “I’m here. I’m the one that was meant to listen to you.” And when that happens, the dendrites of one neuron clasp to the axon of another, forming a joint we call a synapse. The two neurons send chemical messengers across the gap of that synapse, rather like lobbing notes to your crush across a crowded classroom.
(Pedantic scientific aside: Yes, synaptic transmission is much, much more complicated than that and the composition of synaptic scaffolding still holds unknowns, etc, etc. It’s still a nice metaphor.)
But what happens to a neuron in isolation?
Take a single neuron, newly born, and place it in a dish, covered with nutrient broth. All alone. What will it do?
A neuron that isn’t sending information, that isn’t communicating, dies. So what happens to our lone neuron in the dish?
It forms a synapse with itself–an auto-synapse. (More commonly referred to as an autapse.) Without anyone else to send its signals to, it sends them to itself. It has to, or it will die.
I’m currently revising a book I wrote a few months ago, where the hero is terrified of his emotions. He thinks they are wrong, wrong, wrong, and shares them with no one.
But you can’t extirpate an entire emotional life. You would die.
So he keeps them to himself, sending them to the deepest part of him and convinces himself that they have disappeared. In sum, he is a neuron that has had to synapse on itself.
So I’m sending him a heroine. She’s holding out her hand, saying “I’m here. I’m the one that was meant to listen to you.”
He only has to reach out and grasp it.